pythongh-134584: Eliminate redundant refcounting from _BINARY_OP_SUBSCR_LIST_INT (pythonGH-142926)

Author: cocolato

Include/internal/pycore_opcode_metadata.h

@@ -2988,6 +2988,24 @@ class Obj:
         for _ in range(TIER2_THRESHOLD+1):
             obj.attr = EvilAttr(obj.__dict__)
 
+    def test_binary_subscr_list_int(self):
+        def testfunc(n):
+            l = [1]
+            x = 0
+            for _ in range(n):
+                y = l[0]
+                x += y
+            return x
+
+        res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
+        self.assertEqual(res, TIER2_THRESHOLD)
+        self.assertIsNotNone(ex)
+        uops = get_opnames(ex)
+
+        self.assertIn("_BINARY_OP_SUBSCR_LIST_INT", uops)
+        self.assertNotIn("_POP_TOP", uops)
+        self.assertNotIn("_POP_TOP_INT", uops)
+        self.assertIn("_POP_TOP_NOP", uops)
 
 def global_identity(x):
     return x

Include/internal/pycore_uop_ids.h

@@ -893,9 +893,9 @@ dummy_func(
         macro(STORE_SLICE) = _SPECIALIZE_STORE_SLICE + _STORE_SLICE;
 
         macro(BINARY_OP_SUBSCR_LIST_INT) =
-            _GUARD_TOS_INT + _GUARD_NOS_LIST + unused/5 + _BINARY_OP_SUBSCR_LIST_INT;
+            _GUARD_TOS_INT + _GUARD_NOS_LIST + unused/5 + _BINARY_OP_SUBSCR_LIST_INT + _POP_TOP_INT + POP_TOP;
 
-        op(_BINARY_OP_SUBSCR_LIST_INT, (list_st, sub_st -- res)) {
+        op(_BINARY_OP_SUBSCR_LIST_INT, (list_st, sub_st -- res, ls, ss)) {
             PyObject *sub = PyStackRef_AsPyObjectBorrow(sub_st);
             PyObject *list = PyStackRef_AsPyObjectBorrow(list_st);
 
@@ -918,7 +918,9 @@ dummy_func(
             res = PyStackRef_FromPyObjectNew(res_o);
 #endif
             STAT_INC(BINARY_OP, hit);
-            DECREF_INPUTS();
+            ls = list_st;
+            ss = sub_st;
+            INPUTS_DEAD();
         }
 
         macro(BINARY_OP_SUBSCR_LIST_SLICE) =

Include/internal/pycore_uop_metadata.h

@@ -1417,6 +1417,12 @@ dummy_func(void) {
         }
     }
 
+    op(_BINARY_OP_SUBSCR_LIST_INT, (list_st, sub_st -- res, ls, ss)) {
+        res = sym_new_unknown(ctx);
+        ls = list_st;
+        ss = sub_st;
+    }
+
 
 // END BYTECODES //